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[Python-ideas] Anonymous namedtuples

Steven D'Aprano steve at pearwood.info
Tue Apr 19 22:48:11 EDT 2016 
On Tue, Apr 19, 2016 at 08:47:13PM +0000, Joseph Martinot-Lagarde wrote:
> > SimpleNamespace is neither a sequence nor a mapping.
> > 
> I don't know the exact definition of a mapping, but to me SimpleNamespace is
> like a dict with restricted keys (valid attributes only) and a nicer syntax.
> `my_dict["key"]` is roughly equivalent to `my_namespace.key`.

That is (I believe) how Javascript and PHP treat it, but they're not 
exactly the best languages to emulate, or at least not blindly.

Attributes and keys represent different concepts. Attributes represent 
an integral part of the object:

dog.tail
me.head
car.engine
book.cover

while keys represent arbitrary (or nearly so) data associated with some 
data collection:

books['The Lord Of The Rings']
kings['Henry VIII']
prisoner[239410]
colours['AliceBlue']


They don't just use different syntaxes, they have different purposes, 
and while it is tempting to (mis)use the shorter attribute syntax for 
key lookups:

colours.AliceBlue

it is risky to conflate the two. Suppose you have a book called 
"update" (presumably a book of experimental poetry by somebody who 
dislikes uppercase letters):

books.update

Either the key shadows the update method, or the method shadows the 
book, or you get an error. All of these scenarios are bad.

I'd consider giving Python an alternate key-lookup syntax purely as 
syntactic sugar:

colours~AliceBlue  # sugar for colours['AliceBlue']
books~update  # books['update']

before I would consider adding a standard library class that conflates 
attribute- and key-lookup. If people want to do this in their own code 
(and I do see the attraction, even if I think it is a bad idea), so be 
it, but the standard library shouldn't encourage it.


-- 
Steve
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